Atmospheric Sciences & Global Change Division Research Highlights

March 2006

Tropical Clouds Hold Clues to Global Climate

This radar reflectivity image from the millimeter wave cloud radar at the ARM Climate Research Facility site in Darwin, Australia, shows a precipitating convective cloud case on January 22, 2006, about one week into the experiment. The distinctive melting layer is visible at about 5 km.

The crew onboard the Southern Surveyor research vessel endured more than a week of rough seas before the winds calmed and research flights over the ship could take place.

Led by Jim Mather, a small cadre of PNNL researchers spent part of their winter "down under" in January and February 2006, to participate in one of the largest research projects ever to take place on Australian soil. The Tropical Warm Pool International Cloud Experiment (TWP-ICE), co-led by scientists sponsored by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program and the Australian Bureau of Meteorology, resulted in one of the most comprehensive data sets ever collected of tropical cloud properties, and the environment in which they are formed.

"These data will be used for years to come as we seek to refine computer models for simulating climate change and forecasting regional weather," said Mather, co-lead for the experiment. "In particular, cirrus clouds associated with the outflow of convective storms are very prevalent in the tropics, and impact the energy exchange between earth and space. Thus, they have a large impact on climate and global weather patterns. The data set obtained through TWP-ICE will significantly advance our understanding of this important component of the climate system."

In addition to revealing the composition of these high altitude clouds, the in-cloud observations will be used to refine the methodologies used to infer cloud microphysical properties from the long-term data collected at the ARM Climate Research Facility sites in the Tropical Western Pacific.

The experiment included twenty missions with multiple aircraft flying at altitudes ranging from 60 feet to 55,000 feet, obtaining critical in situ cloud observations. Some of these data were obtained during flights over the ARM Climate Research Facility site in Darwin, Australia, as well as over the PNNL Atmospheric Remote Sensing Laboratory (PARSL) onboard a ship located about 60 miles west of Darwin in the Timor Sea. These comparative measurements will help scientists to study the difference in cloud processes over land and water, and consider these factors in climate modeling efforts.

Additional PNNL scientists involved with on-the-ground efforts in Darwin included Chuck Long and Tom Ackerman, while Connor Flynn supervised and maintained the PARSL instruments during its three weeks at sea. Chuck and Jim also visited local schools in Darwin to talk to students about the experiment and climate research. In all, an international team of more than 200 scientists, graduate students, and infrastructure staff took part in the field campaign.